CVE-2025-40083 — net/sched: sch_qfq: Fix null-deref in agg_dequeue

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

net/sched: sch_qfq: Fix null-deref in agg_dequeue

To prevent a potential crash in agg_dequeue (net/sched/sch_qfq.c) when cl->qdisc->ops->peek(cl->qdisc) returns NULL, we check the return value before using it, similar to the existing approach in sch_hfsc.c.

To avoid code duplication, the following changes are made:

1. Changed qdisc_warn_nonwc(include/net/pkt_sched.h) into a static inline function.

2. Moved qdisc_peek_len from net/sched/sch_hfsc.c to include/net/pkt_sched.h so that sch_qfq can reuse it.

3. Applied qdisc_peek_len in agg_dequeue to avoid crashing.

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CVE-2025-40083 — net/sched: sch_qfq: Fix null-deref in agg_dequeue